In 1986, a 60-year-old African American woman visited the Marquette University School of Dentistry with a complaint of a vague, dull pain in her lower left quadrant. Tooth No. 19 was extracted 10 years earlier because of extensive decay, and tooth No. 18 had received root canal therapy. A panoramic radiograph revealed the presence of ill-defined, multilocular, mixed (radiopaque-radiolucent) lesions present throughout the lower jaw. She was treated with antibiotics and scheduled for follow-up visits. When the symptoms persisted, tooth No. 18 was re-treated with root canal therapy and a representative biopsy was taken from the left mandibular area. The biopsy showed the presence of chronic osteomyelitis. The patient was treated with antibiotics and was scheduled for periodic check-up visits. In February 1995, she returned with the same symptoms in the left mandible. A panoramic radiograph showed persistence of the mixed radiopaque-radiolucent lesions throughout her mandible; however, the mass on the left side was more radiopaque and had assumed a "cotton wool" appearance. Tooth No. 18 was extracted and a biopsy was taken from the area. After correlating the clinical behavior, radiographic appearance, and histopathologic features, a diagnosis of florid osseous dysplasia with osteitis was made. This case represents a classic example of the difficulty in diagnosing fibro-osseous lesions using radiographic interpretation alone and the need to correlate the clinical, radiographic, and histopathologic features to reach a diagnosis. Additionally, the present case clearly shows treatment problems of an otherwise self-limiting condition when secondary involvement with osteomyelitis is also present. A brief description of the conditions that were included in the differential diagnosis and their management is presented.